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Background and Aim: Several biomechanical and clinical studies have examined the apparent myoelectric silence of the lumbar spine extensor musculature during lumbar flexion from a neutral upright standing posture.

Objective: The purpose of this study was to investigate the relationship between trunk flexibilitiy and flexion relaxation response of the the lumbar erector spinae

Material and Methods: 30 female healthy students were participated in this study which They were arranged in three groups on toe touch test (low flexible,  normal and high flexible).The surface electromyographic from the lumbar erector spinae muscles as well as flexion angle of the trunk, hip and lumbar were recorded. The angle in which electromyographic diminished during flexion and initiated during extension was determined and subjected to one way Anova to determine any significant differences  in the flexion-relaxation response between three groups.

Results: The erector spinae muscles were relaxed in  larger angles during flexion and initiated activity significantly earlier during extension in high flexible group (p<0/001). pearson correlation indicate that there were high correlation between trunk and hip angle during full flexion (r=0/88 p<0/001) and no correlation between trunk and lumbar angle (r=0/1 p< 0.3).

Conclusion: The results indicated that individuals with more flexible trunk , the erector spinae muscles gets relaxed in further angles of the trunk and the hip, furthermore while returing to the upright posture ,this muscle is recruiting sooner than two other groups .the biomechanical basis of this finding relies in ligamentous and passive tissues properties of individuals with different Flexibilities of the trunk which can effect there recruitment pattern of active tissues.

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Background and aim: Spinal injury especially during occupational lifting is one of the most common neuromuscular disorders in the general population of the world. Asymmetric motions of trunk frequent bending and twisting, lifting and forceful activities contribute to spine disorders. Sport as a comprehensive activity might be able to cause less force to the spine and decrease spinal injuries. The purpose of present study was to determine the effect of lifting on motor control pattern during combined symmetric and asymmetric trunk motions on athlete and non-athlete subjects.
Materials and Methods: Seventeen non-athlete female subjects and seventeen athlete female subjects performed to lift four loads ( 5,7,9 ,12 kilogram ) at symmetric and asymmetric conditions. Under each condition temporal parameters of motor control were measured on flexor and extensor of trunk muscles.
Result: In two groups of athletes and non-athletes with increasing load , muscles begin their activity faster ( P<0.05 ). No significant change was found at asymmetric condition. Also, in athletes premotor time of muscles during lifting was less than non-athletes.
Conclusion: With increasing load, according to the feed forward control mechanism and awareness of subjects from amount of loads, muscles quickly prepared to contract for starting the movement. It seems that the response of movement on the neuromotor system of athletes is preprogrammed and automatic due to sport experience. Actually muscles have anticipation activity.

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Background and Aim: In spite of massive knowledge increase and ergonomic correction, lumbar disorders extremely prevail in working environments. Efforts have been made in order to decrease prevalence of musculoskeletal disorders caused by lifting, carrying and pulling down objects by using some belts. The purpose of this research is to determine the effect of lumbo-pelvic belt in symmetrical load lifting on one of motor control indexes.
Materials and Methods: In this research twenty men were asked to lift objects with different weights of 5.5, 7.5, 9.5 and 12.5 kg in position of complete trunk and hips flexion and knees extension using and not using belt and put them on the target desk. Surface Electromyography has been recorded from two pairs of back muscles and three of abdominal muscles. 
Results: Lifting different loads with belt showed significant increase in symmetrical index (p<0.05). 
Conclusion:  Using belt brings about more coordination in trunk agonist and antagonist muscles activity while lifting the loads.  

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Background and Aim: According to clinical observation, foot hyperpronation is very prevalent and may cause malalignment of the lower extremity in which can lead to structural and functional deficits in standing and walking. The aim of this study was to investigate of  foot hyperpronation effect on spine alignment in standing position.

Material and Method: Thirty-five healthy male ranging 18 - 30 years old were participated in this study. Evaluation was performed with two examiner in four standing positions (on the floor, on the wedges angled at 10, 15 and 20 degrees) using motion analysis system (zebris) and each one of measurement methods repeated three times. SPSS version 17.0 and paired t- test and repeated measures were used for statistical analysis.

Results: Significant difference was seen between all modes in sacral angle, pelvic inclination, lumbar lordosis and thoracic kyphosis variables (except between the first and second mode. Finally, with increasing wedge angle, a positive correlation obtained  for the examiners and all variables.

 Conclusions: The results of this study showed with increasing bilateral foot pronation, sacral angle, pelvic inclination, lumbar lordosis and thoracic kyphosis were increased. In fact, each one of them considered a compensatory phenomenon.

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Background and Aim: Multifidus muscle is one of the short and deep posterior Paraspinal muscles, which gives stability to the spine during various activities. Studies have shown that in people with neck pain, weakness and atrophy of neck muscles are major factors in the incidence of neck pain. Measurement of muscle's dimensions by ultrasonography provides an opportunity to be able to objectively assess muscle atrophy or hypertrophy. This study aimed to assess symmetry of cervical multifidus muscle size in females with chronic non-specific neck pain and healthy by ultrasonography apparatus.

Materials & Methods: Twenty five women with unilateral chronic nonspecific neck pain and 25 healthy women were participated in this study. All subjects were employed and more than 4 hours working with computers or paying office in a day. Imaging of the cervical multifidus muscles were done bilaterally in the level of the fourth vertebra. Anterior-Posterior Dimension(APD), Lateral Dimension(LD), Cross-Sectional Area (multiplied of two diameters(APD&LD)) and the Shape ratio (Lateral diameter divided by the Anterior-Posterior diameter(LD/APD)) of the muscle were measured and recorded. 

Results: Multifidus muscle size in patients group was smaller than the healthy group. In patients group, size of multifidus muscle in the painful side was smaller than the opposite side. Asymmetry of muscle size between the two sides, in the patient group was higher than the control group (P < 0.05). The ratio of smaller size to the larger size of the muscle, in the healthy group was higher than the ratio in the patient group (P < 0.05).

Conclusion: In patients group, asymmetry of the muscle size between two sides, also smaller size of the muscle in the painful side, showed that muscle atrophy has happened in the involved side.